The present invention relates to an improved component for a coupling assembly in which a tube is extended and retracted to move a friction surface into and out of engagement with another component of the coupling assembly.
Known coupling assemblies, such as a brake or clutch, include a component having an inflatable annular tube which is mounted on a rigid annular rim. An annular array of friction shoe assemblies is connected with the tube. When fluid pressure is sequentially conducted into and out of the tube, the tube is sequentially extended and retracted to engage the friction shoe assemblies with another coupling assembly component and to disengage the friction shoe assemblies from the other coupling assembly component. Coupling assembly components having this general construction and mode of operation are disclosed in U.S. Pat. Nos. 4,795,013; 5,057,178; 5,086,899; and 5,117,957.
During use of coupling assembly components having this construction for relatively long periods of time at elevated temperatures and/or pressures, voids or bubbles may tend to develop between a fabric reinforcing layer and an elastomeric outer cover layer forming the tube. If the bubble ruptures, contaminants from the operating environment can enter the tube through the rupture with a resulting degradation of the tube. Whether or not the bubble ruptures, friction shoes adjacent to effected areas may not retract properly. This can lead to overheating and eventual failure of the coupling assembly component.
Based on field observation, inspection of used tubes, and laboratory testing, it is believed that the formation of bubbles or voids in the tube is the result of air migrating through elastomeric material of an inner layer of the tube and becoming trapped in the fabric reinforcing layer. It is believed that the air pressure between the reinforcing layer and the outer cover layer may exceed 70 lbs/sq. inch (gauge). When there is anything less than an optimum bond between the cover layer and the reinforcing layer, air pressure in the reinforcing layer is sufficient to cause a bubble to form between the reinforcing layer and the cover layer.